During infection, one fundamental host defence mechanism depends on leukocyte-mediated killing of microbes. Recently, a group of cationic anti-microbial peptides, which are capable of killing various Gram-negative as well as Gram-positive bacteria by membrane disruption, have been implicated as important components of innate host defence systems in a multitude of organisms. These peptides are found in neutrophils and in epithelial cells located at biological boundaries susceptible to infection.
Pathogens appear to be able to overcome this first line of host defence, giving rise to a spectrum of clinically important conditions of an acute as well as a chronic nature. During infections bacteria utilize a combination of various strategies to overcome host defence mechanisms. Bacteria release various proteinases which modulate host specific pathways involving kallikreins, plasminogen, complement, cytokines, antibodies and antiproteinases during acute infection. Production of exotoxins and cell cycle modulating proteins by bacteria has also been reported and illustrates further the variety of pathways aimed at compromising host defence.
Bacteria such as Streptococcus pyogenes readily give rise to wound infections and erysipelas. Pseudomonas aeruginosa, Enterococcus faecalis and Proteus mirabilis are well known to persist in chronic wounds. These bacteria all propagate and multiply in connective tissues rich in proteoglycans (PG).